It is known in the prior art to produce ethyl acrylate by the reaction of ethylene with acrylic acid in the presence of a sulfuric acid catalyst. In this process recovery of a liquid ethyl acrylate product is accomplished by passing the reaction mixture to a vacuum distillation system wherein, at reduced pressures less than atmospheric, the reaction mixture is distilled to obtain a liquid ethyl acrylate product. Also resulting from the vacuum distillation is a gaseous light ends stream containing sulfur dioxide and also containing ethylene, ethyl acrylate and other organic light ends. The sulfur dioxide in the stream derives from the sulfuric acid catalyst used in the reaction of the ethylene and acrylic acid.
Since the distillation is accomplished under vacuum, which is necessarily provided by a vacuum pump (generally also known as a rotary compressor), the gaseous light ends removed as overhead products in the vacuum distillation system must necessarily be drawn into and passed through the vacuum pump. In the type of pump normally utilized for obtaining the vacuum there is generally employed a liquid seal fluid which provides a liquid seal (sometimes referred to as an "oil seal") within the pump whereby the vacuum may be obtained. Thus the vacuum pump must intake both a gaseous stream from the intake line or conduit which is in open communication with the vacuum distillation system, and also a liquid stream comprised of the liquid seal fluid. Within the vacuum pump the gaseous stream and the liquid seal fluid are intimately contacted with each other and then discharged in a single stream as a gas-liquid mixture. For efficient operation the liquid seal fluid must be recovered from the gas-liquid discharge and reused or recycled through the vacuum pump.
In many instances the recovery of the liquid seal fluid from the gas-liquid mixture is relatively easily accomplished by use of a simple separator; however in the above described process for production of ethyl acrylate many problems occur because of the nature of the gaseous light ends stream. More particularly, various components of the light ends stream are absorbed or partially absorbed into the liquid seal fluid and removal of these components cannot be accomplished merely through the use of a separator. In such instances, it is known to utilize distillation to separate absorbed components from the liquid seal fluid. Thus the choice of a liquid to be utilized to provide the liquid seal in the vacuum pump is quite important since various problems in the recovery and recycle of the liquid seal fluid can be eliminated or minimized by selection of the proper liquid. Many liquids have been found not to be suitable because of polymerization, foaming and other problems. It is believed that some of these problems can, at least in part, be attributed to the presence of the sulfur dioxide in the gaseous light ends.
It is thus an object of the present invention to provide and disclose the use of a liquid which performs satisfactorily as a liquid seal fluid for a vacuum pump utilized in the above described recovery of light ends from the ethyl acrylate process. It is an additional object of the present invention to provide an improved process for recovering the light ends stream from the said ethyl acrylate process and provide for recovery of the liquid seal fluid utilized in the vacuum pump providing the reduced pressure for the vacuum distillation system of the ethyl acrylate process. These and additional objects will become apparent from the following description of the present invention.